Sling doesn't warn how many gigabytes per hour its service will use, but based on some quick, back-of-the-envelope math, it's not a small amount.

Sling's minimum network requirement for HD is 1.5 megabits per second; at full blast, that's about 11 megabytes a minute, or 675 megabytes per hour. (Remember, those are minimum requirements; Sling says higher speeds will yield higher quality.) That could add up quickly: A three-hour baseball game could be about 2 gigabytes; 1 hour of HDTV streamed a day could be about 20 gigabytes a month. Not enough to get Comcast's reps knocking down your door, but certainly a nice chip into your monthly allotment.